GitLab

"make binfiles" should allow building ARM binaries more easily.

Factor out common $(ARM_ELF_FLAGS).

Also rewrite some rules using $< and $@, to avoid repeating
filenames. And trim down on the number of rules using patterns
for objcopy (%.elf -> %.bin) and mksunxiboot (%.bin -> %.sunxi).
Signed-off-by: Bernhard Nortmann <bernhard.nortmann@web.de>